How Much Pipe Lagging Do I Need? 15 mm and 22 mm Foam (UK)
Foam pipe lagging slows the heat leaving a pipe. 12 m of 15 mm pipe and 6 m of 22 mm pipe take 14 pieces of 1 m for the smaller and 7 for the larger, with 10% extra for cutting. The pipe lagging calculator counts it for your pipes.
Pieces for a run of pipe
With 10% extra for cutting:
| Length of pipe | 15 mm, 1 m pieces | 22 mm, 1 m pieces | 15 mm, 2 m pieces |
|---|---|---|---|
| 3 m | 4 | 4 | 2 |
| 6 m | 7 | 7 | 4 |
| 10 m | 11 | 11 | 6 |
| 15 m | 17 | 17 | 9 |
| 20 m | 22 | 22 | 11 |
| 30 m | 33 | 33 | 17 |
Pieces for a house
| House | 15 mm pipe | 22 mm pipe | Pieces of 1 m | Joints and corners to tape |
|---|---|---|---|---|
| A flat or a small house | 8 m | 4 m | 14 | 19 |
| A three bedroom house | 12 m | 6 m | 21 | 28 |
| A large house | 30 m | 15 m | 50 | 69 |
Where to lag first
- The loft. Any pipe or tank in the loft is exposed to the coldest air, and the loft insulation keeps the heat from the house away from it.
- The garage and the cellar. Unheated, and often draughty.
- Outside walls and under floors. Pipes that run against the cold.
- Outside taps. Turn off the supply inside and drain the tap before the winter, as well as fitting a cover.
Fitting the lagging
- Choose the size that matches the pipe: it should fit snugly without gaps.
- Open the slit and push it over the pipe, with the slit on the underside or against the wall.
- Butt the pieces tightly and tape the joints, so that the cold air cannot get in.
- Mitre the corners: cut the ends at 45 degrees so they meet without a gap.
- Cover taps and valves with a shaped piece, and leave room to turn them.
What else helps
- Keep the heating on low when you are away, at about 10 to 12°C.
- Know where the stop tap is, and check that it turns.
- Open the loft hatch on a very cold night, so that warm air reaches the pipes in the loft, but do not leave it open for days.
- If a pipe does freeze, turn off the water, thaw it slowly with warmth (never a naked flame), and check for leaks.
See also the loft insulation calculator and the boiler size calculator. These are estimates: measure your own pipes.
Frequently asked questions
How much pipe lagging do I need?
The length of pipe plus about 10% for cutting, divided by the length of a piece: 14 pieces of 1 m for 12 m of 15 mm pipe.
Does lagging stop pipes freezing?
It slows the loss of heat, so a pipe takes longer to freeze, but a long hard frost can still freeze a lagged pipe. Keep the heating on low and know where your stop tap is.
What size lagging do I need?
The same as the pipe: 15 mm lagging on 15 mm pipe and 22 mm on 22 mm pipe.
Which pipes should I lag first?
Pipes in cold places: the loft, the garage, the cellar, under the floor, and any pipe on an outside wall.
Do I need to lag hot pipes too?
Yes, for the pipes that run through cold spaces: it keeps the water warm and saves a little energy. Cold pipes need it most in a cold loft, because they are the ones that burst.
More guides
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and check the Building Regulations and any planning rules for anything structural or close to a boundary.